The present invention relates to an improved linear sliding closure unit for use in discharging molten metal from a container. More particularly, the present invention is directed to such a linear sliding closure unit of the type including a stationary refractory plate having therethrough a discharge outlet aligned with a discharge outlet through the wall of the container, a closure casing adapted to be mounted on the molten metal container, a linearly movable sliding refractory plate having therein at least one discharge opening, a sliding closure member mounting the sliding refractory plate for linear sliding movement relative to the casing and the stationary refractory plate, and structure for urging the sliding refractory plate toward the stationary refractory plate so that respective sliding surfaces thereof are in abutment. During sliding movement of the sliding closure member and the sliding refractory plate, the discharge opening through the sliding refractory plate is moved between an open position aligned with the opening through the stationary refractory plate and a closed position out of such alignment and blocking discharge of molten metal from the container.
In known linear sliding closure units of this type, for example as disclosed in West German DE-OS No. 22 27 501, the stationary fireproof refractory plate is part of a mounting plate which is fastened to the molten metal container. The closure casing contains the sliding closure member and the sliding fireproof refractory plate and is hinged at one of its side walls to the mounting plate. To connect the closure casing and the mounting plate for operational purposes, each side wall of the closure casing has a bent lever closure member. These two members have to be operated at the same time in order to close the casing. This arrangement also results in a tightening of clamping devices between the sliding closure member and the sliding refractory plate. Such clamping devices are in the form of a plurality of pressure springs inserted loosely in the sliding closure member. When the bent lever closure members are opened and the closure casing is swung outwardly, the sliding refractory plate, as well as the stationary refractory plate, can be removed. Only then are the pressure springs accessible for adjustment or replacement. The amount and the distribution of the contact pressure which the pressure springs exert on the sliding refractory plate depend directly on the position of the sliding closure member which moves linearly within the closure casing, and thus depend on the position of the closure casing with respect to the mounting plate. Because the bent lever closure members have a multitude of moving joints and are operated frequently and under conditions of high mechanical stress, it therefore occurs that an unchangeable and accurately repeatable operational position of the closure casing is not possible, or if possible only with considerable effort of control and maintenance. Thus, known linear sliding closure units of this type inherently have the disadvantage of varied and unevenly distributed contact pressure between the sliding refractory plate and the stationary refractory plate.